Causes of Cancer
Cancers are caused by changes in our genes. Each gene contains a string of molecules that act like letters that “spell out” the instructions our cells need to assemble a specific protein. These letters are made of molecules called deoxyribonucleic acids — DNA — and the instructions they spell out are often called the “genetic code”. When our cells “read” a gene’s instructions and produce the gene’s protein or RNA — the gene is said to be ‘expressed’. How a cell grows, develops and behaves is largely controlled by which genes are expressed or “turned on” and which are not. Changes in genes, caused, for example by the loss of or substitution on one DNA latter for another can cause the cell to assemble the protein incorrectly. Sometimes the cell will not be able to make the protein at all. Sometimes the protein will not work as it should. These changes, called mutations, often cause no harm. Sometimes, they can cause the cell to die. But sometimes they can lead to cancer. Usually more than one gene needs to be affected before a cell can become cancerous. Exposure to radiation, some chemicals and other factors in the environment can cause genetic mutations. However, many mutations simply accumulate over time as we age, which is why cancer is more common in the elderly.
In general, cancer-causing mutations involve three types of genes: Oncogenes, Tumor suppressor genes, and DNA repair genes.
Oncogenes are abnormal forms of genes that usually regulate cell growth and differentiation, the process by which a cell matures to become a specific cell type capably of a specific function, such as a liver or kidney cell. These mutated genes often stimulate uncontrolled growth, turning a healthy cell into a cancerous cell.
Tumor suppressor genes
Tumor suppressor genes are genes that normally code for proteins that help prevent a cell from growing uncontrollably. Some tumor suppressor proteins, for example, will actually cause a cell to commit suicide when it becomes abnormal, preventing the cell from growing and spreading. When tumor suppressor genes are mutated so that they no longer make effective proteins, their check on uncontrolled cell growth is lost.
DNA repair genes
DNA repair genes code for proteins that repair DNA when it is copied incorrectly. These proteins, therefore, can fix errors in the gene’s instructions which could cause cancer. Mutations in these DNA-repair genes can impair their ability to prevent cancer-causing mutations. We have two copies of most of our genes, one copy from our mother and the other from our father; therefore it is possible to inherit a gene that increases our risk of cancer. Often, if we inherit a cancer gene from one parent, the good gene from the other parent is enough to prevent it from having a harmful effect. That protection can be lost if a mutation affects the good gene. In other cases, the effect of cancer gene cannot be overridden by the matching gene from the other parent. People who inherit these kinds of genetic changes often develop a syndrome in causes a number of abnormalities. Such inherited syndromes, however, are rare, and in most cases people diagnosed with primary brain tumors do not have one of these syndromes. There are some brain tumors that are caused by genetic changes that are inherited. Patients with these tumors usually have a specific syndrome that includes a number of inherited abnormalities in addition to a higher risk of developing a brain tumor. However, these inherited syndromes are rare, and in most cases, brain tumor patients do not have one of these inherited genetic syndromes.
- Neurofibromatosis type 1 or 2.
- Von Hippel-Lindau disease.
- Tuberous sclerosis.
- Li-Fraumeni syndrome.
- Turcot syndrome type 1 and type 2.
- Klinefelter syndrome.
- Nevoid basal cell carcinoma syndrome.
- Gorlin (basal cell nevus syndrome).
- Multiple endocrine neoplasia (Werner syndrome).
Exposure to high-dose radiation, such as might be given as part of a cancer treatment, has been shown to increase the risk of developing brain tumors and some evidence that exposure to the chemical vinyl chloride poses a risk. Viral infections have been linked some rare forms of brain cancer. However, in many cases the causes of brain tumors are still not known.